Motor vehicles can be moved back into free stock if not invoiced out by using either bulk vehicle progression or within the vehicle availability grid
Vehicle Tracking/Vehicle availability/ Use the tree to drill into the Franchise, model and variant code.
Once the vehicle has been found on the vehicle availability grid right click and select Progress vehicle
Use the drop down and select 'Free stock' in the "Next progress code" and click on OK
Depending on your setup this will cancel the dealer order and move the vehicle back into free stock.
If there are multiple vehicles that need to be moved back to free stock you can use the bulk vehicle progression method as an alternative.